1. Field of the Invention
The present invention relates to a navigation apparatus that calculates the position of a vehicle and displays this position upon a map.
2. Description of Related Art
In the prior art, in a navigation apparatus that displays a road map based upon road data, it is per se known to correct the road data in consideration of the track along which the vehicle actually travels. For example, with the prior art technique disclosed in Patent Document #1 (Japanese Laid-Open Patent Publication 2000-230835), each time the same road is traversed three times or more, road data for correction is generated by performing averaging processing upon the tracks along which the vehicle has traveled. If the deviation between this road data for correction and the original road data is greater than some predetermined permitted value, then the road data is replaced with the road data for correction. By doing this it is ensured that, even if there is a positional error in the road data, this error is corrected, so that it is possible to perform appropriate route guidance without any deviation between the road upon which the vehicle is actually traveling and the road that is displayed.
Furthermore, with the prior art technique disclosed in Patent Document #2 (Japanese Laid-Open Patent Publication H11-23300), the positions of entry points, exit points, center points and so on of curved roads and branching roads are detected on the basis of change of the orientation of the vehicle, and errors in the road data are corrected on the basis of the results of this detection. By doing this, the road data for curved roads and branching roads are corrected.
With the prior art techniques of Patent Documents #1 and #2, if a plurality of roads extend mutually parallel adjacent to one another, while it is possible to correct the road data for the one of these roads upon which the vehicle has traveled, it is not possible to correct the road data for the other roads. Due to this, sometimes it happens that the positional relationship between a road for which the road data has been corrected and a road or roads that extend parallel to this road becomes inverted, and this is not desirable. In this type of case, the problem may arise that mis-matching takes place when next the vehicle travels upon these roads, and that it may not be possible correctly to recognize which one of the roads is being travelled upon.
The present invention has been conceived in consideration of problems such as described above, and its object is to provide a navigation apparatus that is capable of correcting the road data for a plurality of roads that extend mutually parallel in an accurate manner, and that is capable of recognizing the correct road when next the vehicle travels upon one of these roads.